Batteries that employ Li-ion cell chemistry may produce gas when they are improperly charged, shorted or exposed to high temperatures. This gas can cause catastrophic failure, explosion, and/or may compromise the reliability and safety of such batteries. Conventional batteries including carbon and a flammable electrolyte may combust when they are improperly charged, shorted, and/or exposed to high temperature. Current interrupt devices (CIDs) in existing Li-ion cells are generally triggered by excessive gas generation within the Li-ion cells. To this end, a small headspace around the jellyroll is usually included in existing Li-ion cells. Once a cell begins to overcharge, excessive gas generated from overcharge can trigger a bi-stable metallic disk so as to disconnect one of the terminals. In some cases, gassing agents can be added to the cell to generate extra gas in an overcharge state, such as adding Li2CO3 to the positive electrode. However, these gassing agents can also induce unwanted reactions within the cell, thereby increasing the resistance and decreasing the coulombic efficiency of the cell.
An alternative method is to use a bi-stable metallic strip to cause an intentional short circuit in the presence of excessive gas generation due to overcharge. This approach also relies on gas generation from the storage electrodes and therefore can impose similar tradeoffs between safety and cell performance.
CIDs using the above approaches also suffer from accidental triggers. In general, operations of these devices are more dependent on the temperature and pressure of the cell than on the cell voltage. However, the amount of gas generated by the storage electrodes can change significantly over the lifetime of a cell. At a safe cell voltage, an older cell may generate much more gas than a newer cell does. Therefore, CIDs based on internal cell pressure can accidentally trigger even though the cell is operating safely.